Flip-chip technologies are used in particular whenever the space required for the redistribution routing of the semiconductor chip is to be optimized. In this case, generally a number of terminal contacts arranged on one side of the semiconductor chip are connected in an electrically conducting manner to a carrier.
The carrier may be formed for example as a metallic chip carrier and as such be a component part of the semiconductor device.
However, it is similarly possible for the carrier to be formed as a printed circuit board, for example as a PCB substrate, on which one or more semiconductor devices are mounted in a flip-chip arrangement. In this case, the substrate is not a component part of the semiconductor device. On arrangement of this type, provided by International Rectifier of El Segunda, Calif., 90245, USA, under the trade name “DirectFET”, includes a semiconductor device which has on one side solderable metallizations, which are soldered over their entire surface area to corresponding metallizations of a printed circuit board.
FIG. 1 illustrates a portion of a semiconductor device according to the prior art with a terminal contact 10 formed in one piece. The semiconductor chip 1 represented is shown by way of example as a MOSFET.
The semiconductor chip 1 includes a heavily n-doped drain zone 11, on which a lightly n-doped drift zone 14 is arranged. Embedded in the drift zone 14 are a number of p-doped body zones 15, in which highly n-doped source zones 16 are in turn embedded. The body zones 15 and the source zones 16 are arranged on the side of the drift zone 14 that is facing away from the drain zone 11. A gate electrode 12 is arranged such that it is insulated from the semiconductor zones 14, 15, 16 by an insulating layer 17. A metallization 10, formed in one piece, contacts the various source zones 16 and forms their terminal contact 10. The terminal contact 10 is substantially of a flat form and insulated from the gate electrode 12. The gate electrode 12 is in this case configured in such a way that there are clearances for the terminal contact 10 to the source zones 16.
A reduced representation of the semiconductor chip 1 according to FIG. 1 is schematically represented in FIG. 2. The semiconductor chip 1 has on its front side 19 terminal contacts 10, 13 formed over its full surface area and in one piece. The terminal contact 10 corresponds to the terminal contact 10 already known from FIG. 1 and is connected in an electrically conducting manner and over its full surface area to the source zones 16 represented there. A further terminal contact 13 represents the gate terminal of the semiconductor chip 1, which is connected in an electrically conducting manner to the gate electrode 12 represented in FIG. 1. The connection of such a semiconductor chip 1 to a substrate usually takes place by means of a solder layer applied to the terminal contact 10 over its full surface area.
An arrangement of this type has the disadvantage that the considerable heat loss produced in particular in the case of power semiconductor devices in the semiconductor chip is transferred via the solderable metallization areas to the solder layer and the printed circuit board. As a result, the temperature of the solder can rise above its melting point, which may lead to impairment of the soldered connection concerned.
Instances of damage to the printed circuit board can similarly occur if its temperature reaches excessively high values. For example, FR4, a material typically used for printed circuit boards of this type, with four copper layers, has a permissible maximum temperature of about 110° C. Although alternative materials with a higher permissible maximum temperature are available, they are very expensive.
Instead of the soldered connection mentioned, it is also possible in principle to use a bonded connection, for example of gold or aluminum. However, bonded connections of this type also have relatively low permissible maximum temperatures of approximately 150° C. in the case of gold and approximately 175° C. in the case of aluminum as bonding materials.